Two years ago, 1999 British Open champion Mark Calcavecchia was advised by golf officials to stop using the spray.

It is manufactured by an Alabama-based company Sports With Alternatives to Steroids (SWATS), who have links to other major sports in the United States.

Deer velvet

CNN Senior Managing Editor of Medical News Tim Langmaid says the spray, which is also known as deer velvet, is purportedly used to boost strength and endurance, while it also improves immune system function.

A PGA spokesman told CNN that the "matter regarding Mr Singh is pending review" but could not give an indication of how long the investigation would take.

"There is no timetable at the moment," he added

The 49-year-old Singh was scheduled to play in the Phoenix Open in Arizona starting Thursday, but pulled out citing a back injury, the PGA Tour website reported.

Controversy

Singh's illustrious career has in the past been dogged by controversies, not least back in 1985 when he was banned from the Asian Tour over allegations he changed his scorecard to his advantage during a round.

He shrugged off that setback to gradually make his mark, first on the European Tour, then over in the United States, where he has campaigned on the PGA Tour since 1993.

He has won three majors and was the money list winner in 2003, relegating Tiger Woods to second spot.

But the same year, Singh's veiled criticism of women's No.1 Annika Sorenstam for competing against the men in the Colonial tournament led to negative publicity.

However, in 2004 Singh took the No.1 spot in the rankings from Woods and won the PGA Championship, his final major.

Despite his advancing years, he qualifies for the Champions Tour next month, Singh has continued to compete at the highest level of golf and is regularly in the upper reaches of the leader board in PGA events.